The invention relates to optoelectronic semiconductor components. More particularly, the invention pertains to a method for producing an optoelectronic semiconductor component, specifically for applications having very narrow radiation and/or reception characteristics. The components comprise a chip carrier, which has an approximately planar chip carrier surface and on which an optoelectronic semiconductor chip is fastened with predetermined alignment of its optical axis, and a base part, which is assigned to the chip carrier, supports the latter and is produced from a plastic material, the semiconductor chip being electrically conductively connected to at least two electrode terminals routed through the base part, and the semiconductor chip being assigned a lens, which covers over the base part.
Prior art optoelectronic semiconductor components, in particular those which are subject to increased demands with regard to their optical properties, have largely been produced in metal-glass housings. There, the chip carriers are, usually, baseplates produced from metal mounted with a metal cap with a glass lens fitted in. Due to the mounting by means of a metal housing, it has been possible, on the one hand, to ensure a hermetically sealed closure of the housing and, on the other hand, to provide suitability of the optoelectronic semiconductor component for specific high-temperature applications starting from about 150xc2x0 C. The ageing of the semiconductor chip given such a type of mounting was slight since, on account of the metal housing type used, there was essentially no loading on the semiconductor chip on account of directly surrounding material. Finally, it has been possible to configure the optical properties of the semiconductor component favorably on account of the glass lens fitted into the metal cap.
The considerable costs necessarily incurred by the relatively complicated production are regarded as a significant disadvantage of the optoelectronic semiconductor components that have been produced to date. In this case, the metal cap with a glass lens fitted in, which requires a high production outlay, has a particular impact. Furthermore, the semiconductor components mounted in metal-glass housings have problems on account of the adjustment and manufacturing tolerances that must be estimated to be relatively large, with the result that such optoelectronic semiconductor components generally have relatively unfavorable squint angles. These are production-dictated deviations of the optical axis from the mechanical axis of the component. As a result, such semiconductor components can only be used to a limited extent in applications which involve narrow radiation and/or reception characteristics. In the prior art optoelectronic semiconductor components, a larger adjustment play during mounting consequently has an extremely unfavorable effect on the squint angle obtained, given closer tolerance specifications.
Furthermore, mass-produced plastic light-emitting diodes having lesser requirements with regard to the optical qualities are known in which the housing with a baseplate and a cap is cast in one process operation and thus produced in one part. That production process is significantly less expensive than metal-glass housings. However, as a result of the single work operation of the (pressureless) casting production, excessively high adjustment tolerances and thus high squint angles are produced. The optoelectronic semiconductor components produced in such a way have quite unsatisfactory optical properties for specific applications.
There have become known, as disclosed in Patent Abstracts of Japan, Vol. 16, No. 055 (E-1165), Feb. 12, 1992, and JP-A-03254162, a light-emitting diode with a base part made of metal and a plastic cap with a lens part. There, the object is to improve the positioning accuracy and to increase the emission rate.
Reference is also had to Patent Abstracts of Japan, Vol. 11, No. 367 (E-561), Nov. 28, 1987 and JP-A-62139367 and Patent Abstracts of Japan, Vol. 11, No. 312 (E-548), Oct. 12, 1987 and JP-A-62105486, which show further light-emitting diodes with separately configured lens caps.
It is accordingly an object of the invention to provide a method of producing an optoelectronic semiconductor component, which overcomes the above-mentioned disadvantages of the prior art methods of this general type and which provides for a component that, given high requirements on the adjustment tolerances and thus squint angles, can be produced considerably more cost-effectively as compared to the prior art.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of producing an optoelectronic semiconductor component, in particular such a component with very narrow radiation and/or reception characteristics. The method comprises:
providing a chip carrier strip with a multiplicity of successively arranged chip carriers each having a substantially planar chip carrier surface, injection-molding a base part around an individual chip carrier of the multiplicity of chip carriers on the chip carrier strip and at least two electrode terminals extending through the base part;
fastening an optoelectronic semiconductor chip with a given optical axis on the chip carrier surface of the chip carrier;
contacting the optoelectronic semiconductor chip with the at least two electrode terminals extending through the base part;
providing an independent cap produced from plastic material and having a lens with an optical axis, and placing the independent cap on the base part such that the cap and the base part are automatically positioned with respect to one another such that the optical axis of the lens and the optical axis of the semiconductor chip substantially coincide; and
permanently fastening the cap to the base part.
In accordance with an added feature of the invention, the step of providing the independent cap comprises producing the cap as a separate structural part in an injection molding operation.
In accordance with an additional feature of the invention, a lens covering is produced between the base part and the cap, the lens covering the semiconductor chip.
In accordance with another feature of the invention, an individual optoelectronic semiconductor component is separated from the chip carrier strip only subsequently to the steps of injection-molding, fastening the semiconductor chip on the chip carrier surface, and contacting the semiconductor chip with the electrode terminals.
In accordance with a further feature of the invention, the cap is provided with a holding means and the holding means is positively locked (form-locked) to a support of the base part by placing the cap onto the base part and mutually engaging the holding means and the support, and forming the holding means and the support such that when the cap is placed onto the base part the optical axes of the lens and the semiconductor chip are automatically aligned with one another.
In other words, the objects of the invention are satisfied in that the independently configured cap produced from plastic material is produced as a separate structural part by means of an injection molding operation. The base part is produced in an injection molding operation of a chip carrier from a multiplicity of chip carriers arranged successively in a chip carrier strip. An optoelectronic semiconductor component is separated from the chip carrier strip only after the base part has been produced, after the semiconductor chip has been fastened on the chip carrier surface by means of bonding, and after the semiconductor chip has been contacted with the electrode terminals. The carrier strip encapsulated by injection molding may be produced and processed in an endless manner, so-called reel-to-reel technique. Overall, it is possible in this way to realize cost-effective mounting of the component with very close electro-optical parameter tolerances.
In accordance with a preferred embodiment of the invention, the lens covering the base part is a part of an independently configured cap produced from plastic material, the cap having a holding means for a positively locking mechanical connection to a support of the base part, in such a way that when the cap is placed onto the base part, the holding means and the support alternately engage with one another. The holding means and the support are configured in such a way that when the cap is placed onto the base part, the cap and the base part are automatically positioned with respect to one another such that the optical axes of the lens and of the semiconductor chip coincide at least approximately.
Due to the fact that the base part supporting the chip carrier and the cap with the integrated lens (with the cap placed onto the base part) are produced as two separate plastic structural parts each produced by injection molding, it is possible to produce an optoelectronic semiconductor component significantly more cost-effectively. In fact, the cost savings is by approximately a factor of 10, compared with the prior art components, without accepting losses in the optical properties of the semiconductor component. The two separately produced structural parts can be joined to one another automatically in an substantially play-free manner, with the result that the semiconductor component according to the invention has only extremely small adjustment tolerances and thus extremely small squint angles. The optoelectronic semiconductor component according to the invention is therefore outstandingly suitable for applications having very narrow radiation and/or reception characteristics. The production of the lens, integrated in the cap, from plastic furthermore enables lens shapes which can be produced significantly more accurately than glass lenses, and therefore better optical properties of the lens. The effect that can be achieved by means of a suitable configuration of cap and base part is that when the cap is placed onto the base part, they are automatically positioned and/or centered with respect to one another.
In accordance with again an added feature of the invention, the cap and the base part are cylindrically symmetrical. Their axes of symmetry run concentrically with respect to one another and each coincide with the optical axes of lens and semiconductor chip. Furthermore, the holding means of the cap and the support of the base part are adapted and/or designed for a positively locking connection. In accordance with again a further feature of the invention, the holding means and the support are designed in such a way that when the cap and the base part are joined, they are automatically positioned with respect to one another in such a way as to ensure stable and substantially play-free symmetrical positioning of the cap and the base part.
In accordance with yet another feature of the invention, the cap and the base part are mechanically alignment by forming the support of the base part, on its outer circumference, with a peripheral abutment surface, which supports the holding means of the cap (when the cap is placed on the base part).
The holding means and support which are assigned to the positively locking mechanical connection of cap and base part, which connection can be released in the axial direction, are formed by projections and grooved recesses which are formed alternately and peripherally on both parts. Alternatively, the holding means and support, for mutual alignment of cap and base part in the circumferential direction, are formed by additional, radial projections and recesses which are arranged alternately on both parts and are formed to a limited extent in the circumferential direction.
In accordance with another feature of the invention, the holding means of the cap is provided with a resilient protrusion, and the support of the base part is formed with a complementary notch or groove, for automatically fastening the cap to the base part in a mounting position.
Moreover, for the further configuration of the optical properties of the component or merely for the purpose of protecting the semiconductor chip, the production method may include a step of placing a lens covering or lens-shaped chip covering between the base part and the cap. That lens covering may be produced from a light-transmitting plastic material which, in particular, has an optical filter material.
Furthermore, the base part may be produced from a plastic material which increases the absorption of incident scattered light. In particular, the base material may be colored with a black coloring substance. The shaping of the base part produced from plastic may be chosen such that in addition to the suitability for fastening the cap, a reflector is formed around the semiconductor chip and the optical properties of the component are concomitantly determined in a favorable manner. Furthermore, a reflector assigned to the semiconductor chip may be provided inside the base part for the purpose of improving the radiation properties of the component.
The form of the lens integrated in the cap produced from plastic may be of variable configuration, in a simple and cost-effective manner, depending on desired optical properties of the component. Thus, for example, the cap may have an integrated Fresnel lens, with the result that optoelectronic components having a particularly small structural height and very narrow-angled radiation and/or reception characteristics can advantageously be realized.
In total, the production method according to the invention enables the optical system of the component to be configured in a very differentiated and precise manner.
In accordance with yet another feature of the invention, the production of the base part is from plastic materials which are high-temperature-resistant, soldering-resistant and with which the chip carrier and the soldering connections or electrode terminals are encapsulated by injection molding. The plastic material may in this case be, in particular, a thermoplastic, such as, for example, LCP=liquid crystal polymers, PPA=polyphthalamide, or polysulfone or similar material. Furthermore, thermosetting plastic materials are also possible as the plastic material of the base part; they will generally be more expensive than thermoplastics and are probably less suitable for high-temperature applications.
The material of the cap which integrally comprises the lens of the component may be, for example, a polycarbonate material which may be optically clear and thus fully transparent, or, for the purposes of filtering light of a specific wavelength, may be colored or provided with specific absorptive materials.
The material of the lens covering or lens-shaped chip covering above the semiconductor chip may preferably be resin or silicone.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of producing an optoelectronic semiconductor component it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.